public static Option <T> find <T>(HashSet <T> set, T value) => set.Find(value);
public static Option <T> find <EqT, T>(HashSet <EqT, T> set, T value) where EqT : struct, Eq <T> => set.Find(value);
public static Option <T> find <T>(HashSet <T> set, T value) => set.Find(value);
public static Option <T> find <EqT, T>(HashSet <EqT, T> set, T value) where EqT : struct, Eq <T> => set.Find(value);